1. Field of the Invention
This invention relates to an image stabilizing apparatus for deflecting a light beam by moving an optical member disposed in an optical path, thereby effecting image stabilization.
2. Related Background Art
There are U.S. Pat. No. 4,914,098 and U.S. patent application Ser. No. 259,787 as apparatuses for the image stabilization of a camera. In the former, there is shown the support of a correction optical system which is light beam deflecting means for image stabilization, and in the latter, there is shown the control thereof. Further, the latter has the following means:
1) means for centering the correction optical system to the home position (the central position in the movable range) prior to the start of image stabilization; and PA1 a) A sudden movement of the finder image field occurs to give a feeling of physical disorder to the photographer; PA1 b) The photographer feels the shock by the reaction of the centering operation; and PA1 c) Centering means and a circuit for sampling and holding a center holding signal are required. PA1 (1) To strengthen the slow center feedback; PA1 (2) To heighten the servo gain (open-loop transfer function) of the feedback loop; and PA1 (3) To detect the average position of the correction optical system during image stabilization and apply a correction signal to the feedback loop.
2) means for creating a centripetal force (hereinafter referred to as the slow center feedback) which decreases the great displacement of the correction optical system caused by great vibration or the panning operation.
Of these, the means 2) is widely useful for popular image stabilizing instruments and is an indispensable technique. On the other hand, the means 1) is a countermeasure for the fact that in the embodiment of the above-mentioned U.S. application, the correction optical systems is urged against a driving cam by a strong spring and is always subjected to a great extraneous force. That is, to drive the correction optical system near the central position in the movable range, the slow center feedback action alone mentioned under item 2) above is insufficient.
However, the above-mentioned patent application suffers from the following disadvantages for the centering operation before the start of image stabilization:
In order to eliminate these disadvantages, Applicant further filed Japanese Laid-Open Patent Application No. 3-37619.
The invention of this application is such that the bearing force of a correction optical system and a driving cam is dealt with as the internal force between the two and a torque produced in the cam is by said bearing force negated. According to this application, the centering operation mentioned under item 1) above is not necessary and good image stabilization becomes possible by only the slow center feedback mentioned under item 2) above.
However, again in the apparatus of the above-mentioned Japanese Laid-Open Patent Application No. 3-37619, the average position of the correction optical system during image stabilization creates some deviation relative to the origin position, because in the above-mentioned application, the influence of the urging spring force against the cam is eliminated, but the influence of gravity by the mass of the correction optical system remains and this acts as disturbance on a feedback loop. To eliminate the problem of this deviation of the average position by gravity, the following method would occur to mind:
However, the method (1) adversely affects the image stabilizing ability of low frequency, and the method (2) causes the oscillation of the feedback loop and therefore, both of these methods have a limit in countermeasure.
Also, the method (3), as shown in the known example of Japanese Patent Publication No. 56-45124, the mean value of the time of the displacement of the correction optical system is detected and the correction thereof conforming to the amount of vibration is applied, and this leads to the problem that a certain time is inevitable until this action begins to work. There is also the problem that correction is effected even when the photographer effects panning or the like and great displacement occurs to the correction optical system.
Also, in this apparatus, when deviation in one direction occurs for a long time due to panning or the like, correction is effected with the time length of this deviation also taken into account and therefore, for example, only the steady deviation by gravity or the like is not strictly corrected, but this apparatus was, as it were, a modification of the slow center feedback.